1. Field
The present technology relates to methods and systems for improving the stress modeling of integrated circuits through improved modeling of material conversions such as oxidation, silicidation, and amorphization and epitaxial recrystallization of semiconductors.
2. Description of Related Art
Methods have been developed to model the impact of stress on the behavior of integrated circuit devices at the level of individual transistors. These methods include, for example, full-scale analysis with a Technology Computer Aided Design (TCAD) system; and a method described in U.S. patent application Ser. No. 11/291,294, filed Dec. 1, 2005, incorporated herein by reference.
Behaviors characterized by the various methods for analyzing stress impact at the level of individual transistors can be used to derive circuit level parameters (e.g. SPICE parameters) of the device for subsequent analysis of the circuit consisting of multiple transistors. Such analysis can help predict whether the circuit will operate as intended, and with what margins, or whether the design or manufacturing process or layout need to be revised. For transistors affected by stress caused by shallow trench isolation (STI) regions in proximity to transistor channel regions, revisions can often be made by applying certain general rules-of-thumb, such as increasing the size of any transistor that, according to the stress analysis, turns out to be weaker than expected. Other techniques can also be used to either to relax known undesirable stress, or to introduce known desirable stress, or merely to improve uniformity throughout the layout. See U.S. Patent Publication No. 2007-0202663, incorporated herein by reference.
As integrated circuit scaling shrinks the transistors and the spacing between them, three-dimensional (3D) stress modeling becomes necessary to accurately estimate stress distribution in the transistors and in between the transistors.
Prior stress modeling tools operating in 2D rather than 3D have been able to perform stress modeling with a rigorous model that moves the boundaries of the material(s) undergoing a material conversion. For example, in oxidation, a semiconductor bulk, e.g. silicon, reacts with a dissolved oxidant at the semiconductor-oxide interface, consuming and converting semiconductor bulk material into oxide bulk material. To reflect this consumption and conversion, the boundary between the semiconductor bulk material and the oxide bulk material is moved. The stress model is then applied to the semiconductor bulk material and the oxide bulk material according to this new boundary.
However, transitioning of this rigorous model from 2D to 3D has been unreliable; the 3D stress modeling breaks in the face of the much more demanding problems in 3D. In 2D stress modeling, the different materials occupy 2D spaces, and the boundaries between different materials are lines (requiring 2D description to locate them among the spaces occupied by the different materials). But in 3D stress modeling, the different materials occupy 3D volumes, and the boundaries between different materials are surfaces (requiring 3D description to locate them among the volumes occupied by the different materials). So 3D stress modeling has been unreliable because of the significantly more demanding problems of modeling different materials occupying 3D volumes rather than 2D areas, and the surface boundaries between different materials rather than line boundaries. Also, 3D stress modeling has been unreliable because these 3D volumes occupied by different materials and the surface boundaries between different materials, must change in time to accurately model the ongoing material conversion in time. Accordingly, at present 3D stress modeling fails to rigorously model conversion between different materials.
Historically, 2D modeling has successfully modeled the movement of boundaries between different materials participating in a material conversion. Accordingly, those of skill in the art continue to apply the rigor of modeling this boundary movement, which has been successfully applied in 2D stress modeling, to ongoing attempts to perform 3D stress modeling.